Electric control system



July 16,1946. BQUCKE 2,404,160

I ELECTRIC CONTROL SYSTEM Filed June 14, 1939 2 Sheets-Sheet 1 VVIVVI 64A, F. g E 290+ AMPLIFIER v INVENTOR. HEINZ Boucm';

ATTORNEY.

July 16, 194

H. BOUCKE ELECTRIC CONTROL SYSTEM Filed June 14, 1939 2 Sheets-Shed 2AMPLIFIER FIC3.6

INVENT OR.

RECEIVER HEINZ BOUCKE F'IG.7.

ATTORNEY.

Patented July 16, 1946 ELECTRIC CONTROL SYSTEIVI Heinz Boucke,Berlin-Charlottenburg 2, Germany,

assignor, by mesne assignments, to Patents Research Corporation, NewYork, N. Y., a corporation of New York Application J um: 14, 1939,Serial No. 278,993 In Germany June25, 1938 11 Claims. 1

The present invention relates to improvements in electric controlsystems and methods of operating the same, more particularly toarrangements employed in amplifiers for. oscillatory signal energy whichmay be of low, medium and high frequency for controlling acharacteristic of the output energy in dependence upon variation of thesame or a different characteristic of the input energy to be amplified.Control systems of this type serve various uses especially to improvethe efficiency and/or quality of the reproduction of sound or otheroscillatory signal energy.

The most frequent use of control arrangements of the above type in bothhigh frequency and low frequency amplifiers is in the form of automaticgain or volume control (AVC) involving the employment of a controllingpotential obtained by rectifying and averaging a portion of the signalenergy to be amplified. I

Automatic gain control systems serving to regulate the output volume independence upon variations of input signal strength and otherarrangements of this nature, such as automatic frequency control, bandwidth control arrangements in radio receivers, volume contraction andvolume expansion systems in transmitters, receivers and amplifiers andVarious other control arrangements, generally involve the use of acontrol potential or current obtained by averaging a portion of theignal energy being amplified such as by rectification and subsequentfiltering. The speed of the regulating action in arrangements of thistypeis determined by the time constant of the filter employed forsmoothing or steadying the rectified potential.

It has already been proposed heretofore to employ a plurality of controlpotentials acting with different speeds or time constants to producecertain desirable effects and advantages. Thus it ha been suggestedtoreduce the effect of short interfering impulses by momentarilyreducing the amplification in a receiver equipped with automatic volumecontrol by the aid of an additional control potential acting withreduced time delay.

It is an object of the present invention to proserving to transmit again control potential in an amplifier directly in dependence upon theamplitude of the signals being amplified.

- Still a further object is to control the time constant of the filterin the regulating channel transmitting an automatic volume controlpotential in "an amplifierdirectly in proportionto the degree or rangeof the automatic volume control. Another object is to control the timeconstant of the smoothing filter in the regulating channel fortransmitting a volume control potential in an amplifier directly inproportion to the amplitude ratio of different frequency or groups offrequency component ofthe oscill'atory signal energy to be amplified. a

A further object is to control the time constant of the smoothing filterin the regulating channel for transmitting a volume control potential inan amplifier directly in proportion .to the speed or rate of change ofthe amplitude of the input signal energy applied to the amplifier Stillanother object is to control the time constant of the filter in theregulating channel for transmitting an atuomatic gain control potentialin an audio frequency amplifier. directly in dependence upon theadjustment of a frequency disvide means for and a method of timeconstant energy in an amplifier is obtained ina most efiicient and easymanner.

A more specific object is to control the time constant of the smoothingfilter'in a regulating channel transmitting a controlling potential orcriminating network adapted to modify the quality of the sounds producedin a translating device energized by the amplifierv output.

A further object is to control the time constant of the filter in theregulating channel for transmitting an automatic frequency controlpotential in a radio. receiver equipped, with an automatic tuningarrangement, orin other Words to control the speed or quickness ofaction of the frequency control directly in dependence 'upon thestrength of the radio signals being received.

Still a further object is to control the time constant of the filter inthe regulating channel for transmitting a potentialor current in anaudio frequency. amplifier adapted to compress or expand the dynamic orintensity range of the audio signals being amplified directly independence upon the average signal amplitude.

With theforegoing and other objects which will become apparent. as ,7the following description proceeds, in view the inventioncontemplatesthe provision of mean to render the: time to establish acontrol effect upon changes of a variable current to an element adaptedto vary the transcharacteristic of the amplifier; or of the energy beingamplified, or any other cause. hereinafter referred to as attack timeand/or the time to remove the control effect after cessation of thecause, hereinafter called recovery time directly dependent upon the sameor another characteristic of theamplifier or the energy tobe amplified,

by automatically adjusting an element of the filter r smoothing networkarranged in the channel transmitting the control potential. Theinvention both as regards its design and:- arrangement of circuitelements as well a function and operation will become more apparent,from the following detailed description taken with reference to theaccompanying drawings formingpart of this specification and wherein:

Figure 1 shows for the sake "of illustration 2.

.well known rectifier and filter circuit forproducing and dischargeimpedances preferably although not limitatively consist of ohmic resis-"tors. -"Th'eymay' be entirely or in part inductive ing a controlpotential by averaging a portion .of

the signal energy to be controlled,

Figure 2 illustrates one wayof controlling the time constant or speed ofthe controlling action in a purely electrical manner proposed'by theinvention, I

Figure-ashows a filter circuitsuited for use in a low frequency such asanaudio amplifier for obtaining volume compressionor expansion with thetime constant or speedof the control action depending-upon the-degreeorrange of .gain' .con-

trol! V V Figure {4 illustrates an exemplification of a variable speedgain control in dependence upon the rate of change of-theinputsignalamplitude applied to an amplifier, I I v Figures 4A and 4Billustrate further exemplifications of -variable gain control systemsembody ing the principles of the invention.

.Figure 5 is :acircuit diagram illustrating: an exemplification forvariable speed gain control in dependence uponth tonecontrol adjustmentin an amplifier,

. is .shown a combined rectifier rand filtenrgircuit of well a known.construction for. producing a 'control potential. from aportion ofthetmain zsignal energy to be amplifiedor translated. The.;en-

ergy extracted from the mainrsignalpircuitsuch' as .a receiver .oramplifieris :applied by :way of input terminalsv a-;-b: andtal couplingtransformer It] to a rectifier. suchcasadiode rectifierIIrconnectedacross the transformer secondary inseries with an impedance I2: and acondenser :I3. A further impedance I4 is shunted across :thexzondenserI3. The control or regulating potential 6r is derived fromthe oppositeends -of the-impedance I4 and serves toinfluencea regulating device byway of the output' terminalscd such as. an element. adapted to. controlthe amplifying gain; the band width, tuning adjustment, or any othercharacteristic of thereceiver or amplifierin' a'manner well known in theart.

I "Thei'filter' for; smoothing thecontrol potential ei-1v comprises ingeneral-'a smoothingcondenser I3 in series with a charging impedance I2and I stantof the filter.

reactances. *Thecharging resistance in conjunction with the dischargeresistance determines essentially'the attack time of the regulationwhile therecove'ry time is essentially determined by the *sizeofthedischarge resistance and the smoothductance elements. For this purposeany. one of the known devices-maybe employed such as arrangements forv.step-by-step variation -.of a -.capacity, a resister, or inductanceelement by means of suitable-switching arrangements .or .by

gradualadjustmentof one .onmoreof these .values in anysuitable manner.rA gradualiadjustment may be effected bymecham'cal orelectrical meanssuch as by th emplo-ymentpf electronic valves serving asvariableimpedances .orby means .of-a magnetic reactor provided withIan-auxiliary magnetizationlcircuit.

According to theimprovements of the present invention the controlof-thefilter .timeconstant or the speed of the control ctioninarr-angements 0f the .aforementioned character 'isefiectedrautomatically and. independenc upon a variable characteristic.or :adjusting operation. in thereceiver or amplifier. 'In case'thatthecontrol of the .timenconstant of the filter in the regulating channelcauses 'a variation of the average 7 value of the-control potential,suitable compensating means tcmayzbe employed. to 'elimi nate thisdefect partly or entirely.

'In Figure *2 there .'.is shown a vwayaofeele'ctric control of thetime-:constantof the-filter orthe speed of action not la controlpotential ei ;transmitted through I the filter in ;:.proportion. to.another. auxiliary:controlzpotentialvet. .Therezis .provided for thispurpose a'vacuum tube; Iizsuchaas a triode or a tube of anyotherssuitabl zconstruction serving; as a variable impedance shuntedacross: the output: or: discharge resistance I 4. The impedance -of thetube). is variedin accordance with vthe controlling potential letapplied :to'the .grid or other control"elementinra manner wellunderstood, resulting in a variation i of '1 the tube impedance and.in'turnofthe recovery-:timezcon- In? agsimilar mannerithe .-re-

sistance I 2 may becontrolledft'o adjust the attack time constant or thespeed with 'whichrthe control efiect is.established. Other variableimpedances suited for electrical 'or mechanical :control may be' usedfor' the" purpose 'ofthe invention in vantages of a timeconstantcontrol' 'as'proposed by the invention.

According 1 to i one embodiment, the time constant maybeautomaticallycontrolled in dependence upon the degree or range ofautomatic regulation in anamplifier especially for controlling theintensity range of the amplification such as for volume compression andexpansion. As is known, in arrangements of this latter type the attackand the recovery time constants are chosen by a compromise on the basisof the fact that if the tim constants are too low non-linear distortionwill result, while with time constants being too high dynamic distortionwill occur in the output signal of the amplifier. The non-lineardistortions increase with increasing degree of regulation. Inasmuch asthe degree of regulation is usually not fixed, but may be chosen byoperating an adjusting knob or the like, it is proposed to decrease'oneor both time constants of the filter in the regulating channelautomatically with the decrease of the degree of regulation. In thismanner a desired minimum of both distortionand time delay of theregulating action is ensured for the different ranges or degrees ofregulation.

An arrangement of this type is illustrated by the circuit diagramaccording to Figure 3. In the latter, the smoothing impedances l2 and I4are constituted by variable resistors, preferably of the rotary or anyother suitable type arranged for uni-control by means of a singleoperating element or knob indicated at H, whereby both re-- sistancesmay be increased or decreased simultaneously thereby correspondinglyvarying the attack and recovery time, respectively, for the controlpotential. In the example shown, the cornmon operating element (I'D isextended to simultaneously adjust an element for controlling the degreeof regulation such as a potentiometer 16 connected across the outputterminals and serving to control the magnitude of the control potentialer and in turn the degree or range of the automatic gain control. Inthis manner the speed of regulation is automatically varied in directproportion to the degree or range of the regulating action.

In certain cases it may be advantageous to increase the time constantsor to decrease the speed of the regulating action with increasing degreeor range of regulation in the interest of a better filtering action andin view of the fact that for small degrees of regulation the dynamicdelay is less disturbing than with the higher regulating degrees.

If the degree of regulation is varied by a step switch, the resistors 12and 14 may be constructed and adapted thereto in a manner wellunderstood.

According to another embodiment, the time constant may be varied independence upon the averageQvolume of the signal being received oramplified. Thus,'if the average signal strength is high, the inherentdistortion of the amplifier will be high also in which case it isrecommendable to increase the time constant for the regulation in orderto prevent a further increase of the over-all distortion. The control ofthe time constant or smoothing action in dependence upon the averagesignal strength may be effected for instance by varying one or more ofthe filter elements, in particular the charging and/or dischargeresistance automatically together with the adjustment of a volumecontrol regulator in a desired sense. An arrangement of-this type may bederived from Figure 3 by replacing the potential divider I6 by the usualvariable volume control resistor employed in amplifiers such as in radioreceivers and similar amplifier systems,

Another exemplification of the invention consists in varying the attackand/or recovery time in systems for automatic volume compression andexpansion in dependence upon the relative'amplitude of differentfrequencies or groups of frequencies of the oscillatory signal energy tobe.

amplified. Thus, it has been found advantageous to operatively connectthe variable resistors for influencing the charging and dischargingperiods such as shown in Figure 2 with artone control device in such amanneras to increase the filtering action or decrease the speed of thecontrol with increasing relative strength of the lower soundfrequencies. This dependence may also be accomplished in a purelyelectrical manner asis' understood from the above.

According to a further feature of the invena tion, the time constant isrendered dependent upon. the frequency distribution of the audio orother low frequency signal to be amp-lifiedby dividing the signal bandinto two groups; on

group of lower and higher frequencies predominate over the other. 'Bythe aid of the thus obtained auxiliary control potential (8t) which, if

desirable, may be converted into a control current, theltime constant ofthe control potential proper (er) is then regulated by varying themagnitude of the charging and/or discharge resist-' ance in. any of theabove described'manners. Thus; the control according to Figure 2-may beeffected by shunting an electron valve across the' discharge resistanceand controlling the grid of the valve by the auxiliary (6t) potentialobtaine in the manner described above. I

An arrangement of the latter type is shown in Fig. 4A, wherein separateenergy portions are derived from the secondaries 20' and 22' oftransformer 2i? and applied to diode rectifiersl I and H by way ofaloW-pass filter l2, I3 and a high-pass filter i2", 13, respectively.The rectified potentials developed by the diodeload resistors H'and- M"are combined differentially to produce a control potential et. Thelatter is applied to the grid of tube I 5 for varying the time constantof the filter l2, l3, M for the gain con-- trol potential er to obtain avariably delayed con trolling action dependent upon the amplitude ratiobetween the low and high frequency components of the signal energy beingamplified.

The variation of the discharge resistance in the above described mannermay entail a variation of the absolutemagnitude of the control potentialand in turn a change of the degree of regulation; that is, the latterwill become less if the recovery time is decreased. Since, however, ingeneral the recovery time in automatic volume compression and expansionsystems is chosen substantially higher than the attack may also beeliminated by simultaneously decreasing the discharge resistance and/orthe resistance of the rectifier by shunting. avariablev resistanceacross: the'latter or in any other suitable. manner.

In Fig. 43, there is shown a system of this type for varying the timeconstant of a control potential in dependence upon the average volume.of the. signal energy being transmitted or amplified. There is shown inblock diagram form an amplifier l of a radio receiver or the likeembodying a volume control resistor it of well known design and acommonoperating member indicated at ll for simultaneously adjusting the volumecontrol, the discharge resistor l4 and the charging resistor I2 of asmoothing filter in the circuit producing the control or regulatingpotential 6r.

In addition, means are shown in Fig. 43 to compensate for the effect ofthe discharge resistor M on the amplitude of the. cpntrol potential erbythe provisionof a further variable resistor' 1:8 shunting the rectifierU and arranged for unicontrol with the remaining resistors as shown. Inan arrangement of this type, the time A the speed or rate of change ofthe intensity variations of human speech or a musical selection. In thelatter case, slow intensity variations will cause a more eificientfiltering-resulting in a decrease ofdistortion. In order to carry outthe desired control of the time constant or filtering in accordance withthe rate of change of the amplitude variations a special auxiliarypoten-' tial is required representative. of this relation.

This auxiliary potentialmay be obtained by producing a regulatingpotential. varying according to the intensity changes of the. originalsound" or other signals and to derive from thispotential a furtherpotential by electrical. differentiation which will thus vary accordingto the rate of change of the original regulating potential. Z V

The auxiliary control potential may be utilized to control the timeconstants by controlling one or more electron valves in a mannerunderstood from. the above; The auxiliary control potential is appliedto the. discharge resistance preferably in-such amanner that during the.half waves corresponding to increasingiintensity, the dis-- chargeresistance is reduced, while duringthe half waves correspondingto the.periods of decreasing intensity 2, control ofthe charging resistanceonlytakes place; by applying the respective portions'of the auxiliarypotentials to each of theregulating resistors byway of arectifiersuppressing the undesiredhalf waves: s

In, Figured of the drawings there is. shown an example for influencingthe recovery time constant by means of aeontrolpotential dependent uponthe speed'or rateoi increase of the signal intensity. The'regulating.potential proper er is produced in thesame manner asshown. in theprevious illustrations by applyinga portion of the ignalenergysuch-as-sound currents to. a recti- This. is accomplished.

fierand-filter circuit'l l minals a- -b and the secondary ll of atransformer 29. The regulatingtube t5 shunted across" the dischargeresistance i4 is controlledby the auxiliary control potential et whosehalf waves corresponding to the periods of intensity increase aresuppressed by a rectifier 23. The auxiliary control'potentialet-is-producedbymeansof asecondi rectifier circuit comprising atertiarywinding 22 of the transformer 2&3, rectifier 23 ,v smoothingcondenser.and resistance 25 and having attack and recovery time constants whichare lower than the time constants for the main control potential er; Acondenser 26 and resistance 29 connected across the resistance 25 serveto produce the auxiliary control potential by electricaldifierentiation, i, e. a potential Let) varying according to the rate ofchange of the rectified and filtered potential, the former beingimpressed upon the rectifier 28 in series with coupling resistance 29supplying the auxiliary grid. control potential e1; for the electronicresistance I5. ,If desired a fixed bias may be applied. to the grid in amanner well known.

Still another application of the invention-con sists in the control ofthe time constant of a potential serving to effect automatic tuning. aradio receiver independence upon a control potential varying accordingto the signal strength which may be obtained in a manner similar as inautomatic volume control systems; According to a preferred. arrangement,this control iseffected in such a manner that during strong fadings thetime constant of the tuning control potential isincreased to aconsiderable extent. In this blanketed by the noise level, and though astrong neighboring transmitter may tend to pullover the. tuningadjustmentdueto theautomatic tuning action. The filter for theregulating potential in this case is controlled by the control potentialin such. a manner that the time-constants to establish and remove thecontrol effect are increased during several seconds. This may beaccomplished in an: easy manner by the provision or high ohmic smoothingimpedances shunted by electron valves serving as impedance elements inthe manner described hereinabove. As a result, the tuning will bemaintained constant during-short and strongfading periods but will onlybe switched. over to a neighboring transmitter in case of. prolonged andstrong drifts or fading periods.

The above described arrangement for producing a.- control potentialdependent on the low (audio) frequency signal amplitude and control ofthe time constant depending upon the rate of change of the signalstrength variations, may advantageously be used in a broadcasttransmitter equippedwith means for adjusting the carrier amplitude inproportion to the amplitude of the modulating (audio) signal to improvethe transmission efiiciency. v

In Figures 5 to 7 there are shown specific practical applications ofthe,invention described in the: f .oll'owins Figurezi shows an arrangementfor controlling the time constant for a gain control potential independence upon the adjustment of a tone control device inanaudiofrequency amplifier. The signal currents obtained from any source,

such as a'radio receiver, microphone, pick-up device,-v etc., areappliedto the amplifier 32by way of the input terminals c,f. Theoutput-of to M byway of input ter-.

. 9 the amplifier serves to energize a translating device suchas a loudspeaker 34 by way of a coupling transformer 33. The primary winding ofthe transformer 33 is shunted by a tone control circuit comprising in aknown manner a variable.

resistor 35 and a condenser 35 in series and serving to adjust therelative amplitudes of the low and high audio frequencies resulting in avariation of the quality of the reproduction in a manner wellunderstood. A portion of the audio signal energy is extracted by meansof a tertiary winding 37 of the transformer 33 and averaged by means ofrectifier 38 and smoothing filter comprising a variable chargingresistor 40,

charging condenser, and discharge resistor 42,

to produce a control potential 6r impressed upon a gain control elementof 'the amplifier 32 in .a manner well understood from the above. The

tone control resistor 35 and the smoothing resistor 40 are arranged foruni-control by the aid frequencies, resulting in an improved smoothing.

action and in turn in increased freedom from distortions.

Referring to Figure 6 illustrating a system for time constant control inan amplifier with automatic volume compression, the audio frequencyinput is applied to the. amplifier 43 by way of input terminals cf andthe amplified signal energy applied to a translation device such as acutting device for phonograph recording connected to the outputterminals g-h. A portion of the output energy is a applied to theprimary of a transformer 44 having two secondary windings 45 and B. 5The secondary 45 serves to energize a rectifier 46 and filter comprisingcharging resistor 41, smoothing condenser 48, and dis- 2 charge resistor49 to produce a control potential e1- applied to a gain control elementof the amplifier 43 for compression of the signal intensity range, in amanner well known in the art. There is further shown an electron tubeimpedance A shunted across the charging resistance 4'! and serving tocontrol thecharging period of the smoothing condenser 48. For thispurpose'the grid of the valve 55 is controlled by an; auxiliarypotential er varying according tothe average signal strength andproduced by means of a rectifier 5|, smoothing condenser 52 anddischarge resistance 53 energized by the secondary winding 50 of thetransformer 44. A source of potential 54 such as a dry battery or theequivalent serves to provide a fixed bias for the tube 55, whereby areduction of the tube resistance is started after the signal amplitudeexceeds a predetermined value. In this manner it is possible to reducethe attack time for the compression control with increasing signalstrength, in particular when a predetermined signal strength is reachedwhich may be chosen by suitably proportioning the .eircuit elements.- pv Referring to Figure 7, there is shown an exemplification of theinvention embodiedjin a system for automatic frequency. control commonlyused in radio receivers. The rectangle 56 collectively indicates areceiver preferably of the superheterodyne type having its input excitedby an ground connection 58 and having its output connected to atranslating device such as an image receiver or loud speaker 59 as shownin the drawings. The receiver is equipped with a system for automaticfrequency control known per se and indicated in the drawings only to anextent as is deemed necessary for an understanding of the invention.

A portion of the intermediate'frequency energy extracted from the tunedcircuit 60 is applied to the grid of an amplifier valve Gland theamplified signal energy impressed upon the'tuned output transformer 63.The opposite ends of the. secondary winding of the latter 'are connectedeach to one terminal of a rectifier such as diode rectifiers 64 and 65,respectively,uthe remaining terminals of the rectifier being connectedthrough a pair of equal resistances 66 and 61 in series and shunted bysmoothing condensers 66 and 61', respectively. The center tap'of thesecondary winding 53 is coupled on the onehand to the high potential endof the primary winding and to the junction of the resistors66 and 61through a high frequency choke 0011 on the other hand, whereby in a'known manner the sum and the difference of the primary and secondarypotentials of the transformer 63 are rectified and combined inopposition producing a difierentialpotential between the outer ends ofthe resistances 56 and 61 which potential varies directly in proportionto and depending on the sense of detuning of the transformer 63 relativeto the impressed signal frequency. This tuning control potential is thenapplied'by'way of circuit connections 68 and 69 to a reactance controlelement of the receiver 56 such as the local or heterodyne oscillatorsuited to effect a tuning control in such a manner as to automaticallyadjust the intermediate signal frequency to coincide with the centerresonance frequency of the intermediate frequency amplifier of thereceiver. According to the present improvements there are provided apair of variable impedances in the form of electronic tubes 16, TIshunted across the resistors and 61, respectively, and serving forautomatic control of the time constant for' the frequency controlpotential in dependence upon the carrier amplitude or average strengthof the radio signals being received. For "this purpose the grids of thevalves 16 and l'l are simultaneously controlled by a potentialetproduced by applying another portion of intermediate frequency energyextracted from the'circuit 60 by way of transformer l0 to arectifying'circuit comprising rectifier H shunted by smoothingresistances 12 and 13 in series. The cont'rol potential er is derivedfrom the ends of the res stance 13 shunted by a smoothing condenser 14,while a further fixed bias is applied to the grids of the tubes 16provided by a suitable source such as a battery 15 and acting inoppositionto the rectified potential drop developed across smoothingresistance 13.

In an arrangement of the aforedescribedtyl i the regulatingtime constantfor the automatic frequency adjustment will be normal as-long as thesignal strength remains within a predetermined limit, in that the fixednegative grid bias for the valves 15 and 11 provided by the battery 15iscompensated by the potentialfldrop across resistance 13. "If thesignal strength decreases below this limit the valves 15 and 11 will .beblocked by the negative bias 15, whereby the disr the ener ybeing;translated.

cal ncrey" in Y prising rectif:

1 adau 'il arv-pctential by extracting anda cr a c rsw- 5 charge of thecondensers 55' and fi'l take place through the resistances iand E'Eonlyinsuch a In other words, the speed It will he evident from the abovethat. the invention is not limited to the specific circuits andarrangements of parts. and methods disclosed "herein for illustrationbut that the underlying idea and prineipleof the invention aresusceptible l of numerous. modificationsand variations coming within itsbroader scope and spirit as definedhy the appended claims.

i drawings are to: be regarded accordingly in an illustrative ratherthan in a limiting sense.

The specification and Iolaim; 1-. In; atranslation system foroscillatory signal l cner y,: means for producing an auxiliary poten- 1tial. lay extractin and avera in a pQltion of the {energy beingtranslated, means to utilize said auxiliary potential to automaticallycontrol a con-,7 dition ofxtheenergy being translated; and furthermeansi r' automatically varying the speed of controlof: said all.

iliagry potentialin. direct do? n nd ncc, upon variations of a dine-rentcondition In a ion system fo1"oscil a.torysi d ng an amplifier, means cmrisandfilter means fer-produci ins a portion; cf-thc energy eing r nslted; said tial for- CQIltlOlling-thd gain; f. said amplifier means f rproducing a ur auxiliary poten- 3 tial varying-inproportion tovariations of a difj ferent condition of the energy being amplified,;-and-mcans toutiliz sa d further auxiliary poten- 1 ial. for, cont ollng he m gn de f atl one 1 of. th impeda ce lemen s, of-said nltcr meansIna trans a ion sy tem or oscillat ry s gna ludinegan amplifier, meansomprisine g; and filter means. for producing an aux,-

rectl iliary' potential. by extracting and. ayeragiue a 1 pcr on f the'nersy heing transl fid; s id-filter means comp i ga. netw rk of impcdncc lcr 5 mcnts. nclcctronic device .perativelyfconnccted with at l ast.one of said mpe ance e eme ts, mea s tc-utilize said. a xil a ypotential for n-- trcl inertlae gain of sa mplifier, m ans or Produc nsa. further au iliary pot ntial varyingin proporti n to va iati sci adifferent. condition 3 oi the cn eyh ine amplified, and further mean ito ontrol th impedance. of said el ronic devic in ac or ance. with saidf rthera x li ry po enial, to ary he, time constant of, said fi t r.means 1 n dependence pon. variations of, sai condition- 4. I a, y tem asclaimed claim. w erein said further auxiliary otential vari s with therate of. chan e oithc i nal amplitude. variatio whereby the speed 0i thgain. c ntrol-is vari d in j direct proportion to the rate of. chance.ci. th signal amplitudevariaticns.

5.. In asystcmas claimed in laim 3., wherein said further auxiliar potntial vari sa cording to the relativeamplitudcs of high audlcw frelquency: mponen s of. t e. e er y eing. trailer lated' whereby the speedof gain control is dc.-

creased with increasing relative strength of the low frequencycomponents.

; lter mea s; c mpr sin a twork f i p dan elements, mea s to ut liz saiduxili y Pe eautomatic gain control means to effectcompressionoftheintensity range of the amplifiedaudlo signals, filter means in the gaincontrolcircuit, meansfor producing an auxiliary potential varying inaccordance with theaverage signal amplitude, further means forcontrolling the time constant of said filter means by said auxiliarypotential, whereby the time constant is decreased as the signal strengthis increased, and delay means to limit the control of the time constantof said filter to signal amplitudes in excess of a predetermined minimumlevel;

7; In an audio frequency'amplifier comprisin automatic. gain controlmeans for. compressing the intensity range of the amplified audiosignals, filter means in the gain control circuit compris ing impedanceelements and an electron discharge device opcratively connectcd'vvith'atleast one of i said impedance elements; means to provide a fixed biasfor said electron device, means for producing an auxiliary potentialvarying in proportion to the, average signal amplitude, and meanstoapplyadditional variable bias tosaid electron device by said auxiliarypotential to control the time constant of said filter means; said fixedbias being of such polarity and magnitude that the time constant isdecreased when the Signal amplitude increases beyond a predeterterfering noisewaves of relatively short, period compared to the signalWaves, or toselective 'signal fading conditions, said range controllerincluding a variable gain amplifier in'said; circuit and a controlcircuit including a variable impedance, for automatically adjusting thegain of said amplifier" to, make the amplitude range of he si nals inits output a desired function-of the signal amplituderange, in itsuncut, means to mpr ve the operation of said range controlle comprisingmeans for automatically varyingthe value of said variable impedance toadjust the time. constant oi said control circuit in accordance with therate of variation of the- Waves-lap: plied to. the input of saidamplifier.

10.. In a transmission system, a. rectifier e er,- gized from saidsystem to produce a control volta e, meansfor controlling a transmissioncharacteristic. of said system-in accordanceivith said control voltagc,a filter connecting said rectifier to. said control means forpartiallysmoothing; out

variation i said. controlvoltage, means forad- J'usting the. time.constant of the-filter,,-andsaid adjusting means being a omaticallyactuatedin dependence on adifierent. characteristic oi ignals emanating:from said system. 1

1.1,. In a. transmission system. a re tifier energized from saidsystemto, produce a control-volt. age, means for contro ling. a-. transmissicnh cteristic of said system'in accordancdWith said contr l voltage, afilter connecting said rectifier to. said c ntrol means tor partially mo hing,- out ariations in said control voltage; and mean operciting.- atomatically in p ndence on; variations, in a difierent. characteristic.0: signals in said system. ior'adiusting the fi ter time constant.

- HEINZ BOUCKE.

